This little book has 128 pages of text. After some cosmology and particle physics, discussion of string theory commences on pages 53-57, conintuing on 73-102, 110-111, and 115-125, for a total of 48 pages. Subtract maybe another 25% for amateurish diagrams that do nothing but repeat the text, massive white space, and constant repetition, and you end up with about 36 pages of content on the subject of the title of this book.
I'm not sure who the target audience is for this work. It contains no mathematics beyond addition. It contains sentences such as this: "The nine planets of our solar system, in order of distance from the sun are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto." Or: "Dividing by a number greater than one yields a smaller number." What do you think, maybe 5th graders?
The content is necessarily shallow, tossing out buzzwords, with no continuity, no real explanations. Branes are never actually defined. M-theory is never defined beyond being the theory that ties together all the other string theories. Somehow. I wonder what the "M" stands for.